The invention is in the field of electronic reproduction technology and is directed to an apparatus for pixel-by-pixel and line-by-line, opto-electronic scanning of masters chucked on a scanner drum. Such a scanner drum apparatus, referred to below as a drum scanner, can be designed for scanning black-and-white or chromatic masters in reflected light and/or transmitted light.
A drum scanner for scanning transparency masters is composed, for example, of a rotating, transparent scanner drum onto which a transparency master to be scanned is chucked, of a light source for pixel-by-pixel illumination of the transparency master, and of a scanner element with a scanner objective, a scanner diaphragm and an opto-electronic transducer for converting the scan light the transparency master allows to pass into an image signal that represents the luminance values of the scanned pixels.
The light required for the pixel-by-pixel illumination of the transparency master is, for example, transported from a light source located outside the scanner drum through a light conductor into the hollow-cylindrical interior of the scanner drum and is imaged as a focal spot onto the transparency master therein with a matching objective and a deflection mirror. The scan light modulated with the image content of the transparency master proceeds through the scanner objective into the scanner element located outside the scanner drum and is converted therein into an image signal by opto-electronic conversion.
The scanner element on the one hand and the optical elements on the other hand are respectively secured to an arm of a U-shaped feed support, whereby the arm carrying the optical elements projects into the scanner drum at the end face.
For planar scanning of the transparency master, the feed support moves in the axial direction of the rotating scanner drum.
In order to be able to scan masters having different formats, scanner drums having different diameters usually are delivered together with a drum scanner, these being chucked in the drum scanner dependent on the format of the master to be scanned. In this case, lens systems must be manually interchanged at the feed support for optimum setting of the size of the illumination spot on the transparency master in order to compensate the different radial spacings between the central arm of the feed support and the generated service of the respective scanner drum. For optimum focusing of the brightness-modulated scan light coming from the transparency master onto the scanner diaphragm, the scanner element is equipped with interchangeable lenses that must be manually pivoted into the beam path dependent on the diameter of the scanner drum employed. The employment of such sets of lenses and interchangeable objectives is relatively complicated.
Occasionally, device-specific, optical fine adjustment must also be implemented, for example for compensation of mechanical and/or optical tolerances in the apparatus assembly or when replacing optical components. These fine adjustments are particularly involved when scanner drums having different diameters are employed in a drum scanner.
It is therefore an object of the invention to improve an apparatus for pixel-by-pixel and line-by-line, opto-electronic scanning of masters chucked on scanner drums such that optical adaptations and corrections, particularly given employment of scanner drums having different diameters, can be implemented in a simple way and automatically to the farthest-reaching extent.
According to the present invention, an apparatus is provided for point-by-point and line-by-line, opto-electronic scanning of a master. A scanner drum is provided for chucking a master to be scanned. An illumination unit generates an illumination spot on the master. A scanner objective is provided. The scanner element converts the scan light modulated with a content of the master and focused with the scanner objective into an image signal. A feed support is provided at which the illumination unit, the scanner objective, and the scanner element are arranged, whereby the feed support implements a feed motion in the direction of the rotational axis of the scanner drum for scanning of the master. The illumination unit comprises a light conductor aligned substantially in a direction of a rotational axis of the scanner drum and has a light exit face for generating a light spot and a matching objective for imaging the light spot onto the master as the illumination spot. At least a sub-section of the light conductor is seated inclinable by small angles relative to the rotational axis in the region of the light exit face for fine adjustment of optical beam paths, as a result whereof the illumination spot is displaced on the scanner drum.